PubMed Health⌕ Search

Biomedical subjects

A Vieira

Publications and source records attributed to A Vieira.

At least 19 recordsLinked to original sources
PubMed1992

Automaticity and preattentive processing.

The characteristics of automatized performance resemble those of preattentive processing in some respects. In the context of visual search tasks, these include spatially parallel processing, involuntary calling of attention, learning without awareness, and time-sharing with other tasks. However, this article reports some evidence suggesting that extended practice produces its effects through different mechanisms from those that underlie preattentive processing. The dramatic changes in search rate seem to depend not on the formation of new preattentive detectors for the task-relevant stimuli, nor on learned abstracted procedures for responding quickly and efficiently, but rather on changes that are very specific both to the particular stimuli and to the particular task used in practice. We suggest that the improved performance may depend on the accumulation of separate memory traces for each individual experience of a display (see Logan, 1988), and we show that the traces differ for conjunction search in which stimuli must be individuated and for feature search where a global response to the display is sufficient.

Attention↗
PubMed1991

Heparin sensitivity and resistance in the neonate: an explanation.

Based on in vitro tests, newborns are reported to be both sensitive and resistant to standard heparin (SH) compared to adults. The sensitivity to SH occurs in assays based on de novo thrombin generation, and SH resistance occurs in systems where exogenous thrombin is added to newborn plasma. We hypothesized that this apparent paradox is related to the antithrombin III to (pro) thrombin ratio associated with each test. Since SH catalyses the activity of antithrombin III, any imbalance in the antithrombin III/(pro)thrombin ratio in newborns compared to adults would be amplified by SH. If the ratio of antithrombin III/(pro)thrombin is defined as 1 in adults, in comparison newborns have a ratio of 1.5. We compared how various doses of SH (0.1 to 0.6 u/ml) inhibited the generation of endogenous thrombin in defibrinated newborn (N) and adult (A) plasma. Following contact activation and recalcification of each plasma, thrombin activity was measured using a chromogenic substrate and quantitated by measuring the area under the curve. In the presence of SH, newborn plasma was more sensitive to SH than adult plasma and generated relatively less thrombin (N:6.1 vs A:9.1% sec/u/ml; p less than 0.01). When the ratio of antithrombin III/(pro)thrombin in newborns was altered to 2.5 by exogenous antithrombin III, the SH sensitivity was increased. This plasma now generated no detectable thrombin in the presence of only 0.1 u/ml of SH. In contrast, when the ratio of antithrombin III/(pro) thrombin of the newborn was altered by exogenous prothrombin to 0.6, this plasma now became resistant to SH and generated more thrombin than adults in the presence of SH (N:11.6 vs A:9.1; p less than 0.01). Because of the potential use of low molecular weight heparins (LMWH) in newborns, a LMWH, Choay 222, was also tested in a similar fashion and gave similar results to SH. Thus, the ratio of antithrombin III/(pro)thrombin likely determines the in vitro sensitivity or resistance of newborn plasma to SH and LMWH. There are no clinical studies that determine if newborns require more or less SH than the adult to successfully treat thrombotic complications. Current practice is a simple extrapolation of therapeutic ranges from adults. We speculate that the efficacy and safety of SH in the newborn in vivo can be improved by altering the antithrombin III/(pro)thrombin ratio.

Adult↗
PubMed1991

Therapeutic sleep deprivation and antidepressant medication in patients with major depression.

Although there is a body of literature on the therapeutic efficacy of sleep deprivation (SD) there are only a few investigations in which the relevance of antidepressive medication for the clinical efficacy of SD has been studied. Based on the literature and on our own investigations with major depressed patients it seems that for the day-1 response it does not matter if and what type of antidepressive medication the patient receives. Furthermore, the results of our double blind study reveal that the day-1 response to total sleep deprivation (TSD) is not associated with a clear relationship to the outcome after 4 weeks treatment with either fluvoxamine or maprotiline. On the other hand, our data indicate that the day-2 response to TSD is significantly correlated with a beneficial outcome after subchronic treatment with maprotiline.

Antidepressive Agents↗
PubMed1990

Multiple hormone responses to stimulation with dl-fenfluramine in patients with major depression before and after antidepressive treatment.

The authors investigated 31 drug-free inpatients with major depression using dl-fenfluramine (dl-FEN) as a serotonin probe (fenfluramine stimulation test, FFT). The FFT was performed in the same individuals (intraindividual comparison) with and without application of dl-FEN and before and after antidepressive treatment. Blood samples were analyzed for prolactin, cortisol, thyrotropin (TSH), growth hormone (HGH), dl-FEN and its major metabolite dl-norfenfluramine. There was no difference in the conditions before and after treatment as regards peak plasma levels of dl-FEN. Compared with saline, significant (P less than 0.01) increases were detected for dl-FEN-stimulated cortisol and prolactin values. A significantly (P less than 0.01) lower increase in dl-FEN-stimulated prolactin values was found after treatment compared with the situation before treatment, a finding which was dependent on the type of medication which the patients were receiving at the time when the test procedure took place. Baseline and dl-FEN-stimulated cortisol values were significantly (P less than 0.001) lower and TSH values were significantly (P less than 0.01) higher in the condition after compared with the one before treatment. Patients' mean peak delta prolactin responses to dl-FEN before treatment were significantly (P less than 0.05) correlated with those of patients after subchronic treatment with fluvoxamine. Hormonal responses were neither associated with the severity of the illness nor with a specific psychopathological profile.

Adult↗
PubMed1990

Response to total sleep deprivation before and during treatment with fluvoxamine or maprotiline in patients with major depression--results of a double-blind study.

To test the hypothesis that the antidepressant effects of total sleep deprivation (TSD) are linked to the serotonergic and/or noradrenergic system the authors carried out a double-blind study (fluvoxamine versus maprotiline) in 42 inpatients with endogenous depression (ICD). Patients were randomized to a four-week treatment with either fluvoxamine (100-300 mg/day) or maprotiline (100-300 mg/day). In addition, patients underwent a TSD procedure before and after one week of antidepressant medication. There was a statistically significant reduction of depression ratings (HDRS) in both the fluvoxamine and maprotiline group. The day-1 response to TSD before antidepressive medication was not associated with a clear relationship to the outcome after four weeks of treatment with either fluvoxamine or maprotiline. On the other hand, the day-2 response to TSD was significantly correlated with a good outcome to subchronic treatment with maprotiline. Furthermore, the results of the authors' data suggest that a favorable short-term outcome of TSD may be connected to antidepressants enhancing the serotonergic neurotransmission. The global comparison between fluvoxamine and maprotiline revealed that the group of patients treated with fluvoxamine had a significantly higher efficiency index (CGI) than the maprotiline group; fluvoxamine was rated to be tolerated excellently in 70% of the patients whereas this percentage was only 43% in the maprotiline group. There was also significantly more vertigo and dry mouth in the maprotiline group whereas the fluvoxamine group was rated to have significantly more sleep disturbances during the trial.

Adult↗
PubMed1988

Nocturnal TSH and prolactin secretion during sleep deprivation and prediction of antidepressant response in patients with major depression.

In order to test the hypothesis that changes in the hypothalamic-pituitary axis during sleep deprivation are related to the antidepressant effects of this procedure, we measured thyroid-stimulating hormone (TSH) and prolactin levels in 32 depressed patients at 2:00 AM during a night before, during, and after total sleep deprivation (TSD). TSH levels increased significantly (p less than 0.05) during TSD, and prolactin levels decreased significantly (p less than 0.0001). When we divided the patients into responder and nonresponder groups based on a 30% reduction in the Hamilton Rating Scale, there was no difference between the two groups in their hormone levels on the baseline, TSD, or recovery nights. Changes in prolactin or TSH were not correlated with clinical improvement when the two groups were considered together or in the responder/nonresponder groups separately. Baseline values of both hormones were significantly (p less than 0.01) correlated with their respective levels during TSD and recovery sleep. These findings indicate that the relative levels of nocturnal TSH and prolactin are stable even within acutely depressed individuals and that changes in their levels are not related to the clinical response to sleep deprivation.

Adult↗
PubMed1977

Potentiation of FMD vaccines with polycationic-nucleic acid complexes.

The effect of various polycations on the immune response potentiated with poly I:C was studied. It was found that low molecular weight polycations had no potentiating effect. Polylysine was ineffective whereas protamine was superior to lysozyme, poly-arginine, poly-histidine, DEAE-Dextran and histone. A foot-and-mouth disease trivalent vaccine composed of strains A24 Cruzeiro, O1 Caseros and C2 Resende elicited no immune response in swine when adjuvanted with aluminium hydroxide but was effective when emulsified in oil. In general, the immune response was potentiated ten-fold when the emulsion contained poly I:C. The antibody production was in most cases further potentiated by a factor of ten when the nucleic acid double-strand was complexed with 1 : 10 (w/w) DEAE-Dextran. Protamine was as effective, or perhaps even more, than DEAE-Dextran to this effect. Guinea pigs vaccinated with a water-in-oil emulsion type monovalent C3 vaccine showed an increase in antibody production when the vaccine contained poly I:C or poly I:C complexed with 1 : 10 (w/w) protamine.

Adjuvants, Immunologic↗